Air duct



FIG. 1 is a perspective view, showing the new design for an air duct;

FIG. 2 is a left side view thereof, the right side view being a mirrorimage thereof;

FIG. 3 is a front view thereof;

FIG. 4 is a rear view thereof;

FIG. 5 is a top view thereof; and,

FIG. 6 is a bottom view thereof.

The broken line showing forms no part of the claimed design, and theshading is provided to illustrate contour only and is not an indicationof texture, etc.

The ornamental design for an air duct, as shown and described.